The long range aim of this project is to provide a quantitative analysis of the effects of therapeutic perturbations on the kinetics of tumor growth. The I125-iododeoxyuridine prelabeling technique is now sufficiently refined to permit detailed observations on the in vivo kinetics of tumor cell proliferation, migration, and death in all body compartments. Ideally, the I125 assay should thus permit continuous evaluation of the success of various radiotherapeutic or chemotherapeutic treatment regimens as well as indicating when (and sometimes why) a treatment ceases to be effective. More specifically, the effects of radiation and antimetabolites on tumor growth parameters, as influenced by changes in nutrition, oxygenation, repair capacity, cell concentration, and other variable factors will be studied throughout tumor growth. Attempts will be made to manipulate these factors in such a way (hyperthermia, combined chemotherapy-radioisotope treatments, etc.) that the damage to the tumor cells is maximized while the damage to the host tissues is kept as low as possible. BIBLIOGRAPHIC REFERENCES: Hofer, K.G., Choppin, D.A., and Hofer, M. Effect of hyperthermia on the radiosensitivity of normal and malignant cells in mice. Cancer (in press), l975. Hofer, K.G. Effect of hyperthermia on the radiosensitivity L1210 leukemia cells and Ehrlich ascites cells in vivo. Radiation Res. (in press), l975.